Plane a double ender

Discussion in 'Powerboats' started by Inquisitor, Jun 12, 2010.

  1. Inquisitor
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    Inquisitor Senior Member

    Is it possible to make a symmetric hull (front to back symmetry) that will plane or is the blunt transom required? In other words could a boat plane going forward and backwards?
     
  2. apex1

    apex1 Guest

    With ample power a bathtub can plane, but what would be the sense? Why?

    Most boats have a rudder to change direction.:D
     
  3. Inquisitor
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    Inquisitor Senior Member

    Proa

    Yes, I know... we have that phrase too... with a big enough engine you can make a barn door fly.

    Anyway, one word - Proa.

    Its a little tough running that transom head first. If you are really interested versus finding another EASY pigeon to take shots at...

    It appears to me that there is a large range of speed where a HarryProa's windward hull is above hull speed (~ 7.5 knots w/ LWL/BWL ~ 6) and it finally clears the water (I'm guessing north of 20 knots) where it is creating a lot more drag than it needs to.

    It appears to me that if the hull could gain some characteristics to help it plane, it might lift itself partially out and reduce its drag... maybe considerably. I am way out of my knowledge base... thus, the question.

    Looking at off-shore race boats, maybe steps could be incorporated. But if you were to tell me that the transom break is the primary and the steps are secondary and only 2% of the whole process... I'd happily scratch this itch.

    Sincerely... Thanks.
     
  4. apex1

    apex1 Guest

    That was not my intention, so caalm down.

    A proa is of course another animal than a double ender. And using the right terminology makes it easier to get sensible answers.

    Having no experience with multihulls I will stay out here.

    Regards
    Richard
     
  5. hoytedow
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    hoytedow Wood Butcher

    Would you have gudgeons mounted each end?
     
  6. Inquisitor
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    Inquisitor Senior Member

    I'm not a motor boat guy... what's a gudgeons? Wikipedia told me it was a fish! :(
     
  7. Inquisitor
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    Inquisitor Senior Member

    It looks like my trying to be funny is getting lost in the translation today. Yes, I see that gudgeons are for steering. However...

    I'm only asking about the drag reducing abilities of a hull that planes. And is it possible to make one that is symmetric from front to rear... so that it could plane going either direction. (1) Stability in pitch or roll and (2) steering and (3) powering are not issues that have to be addressed by the hull shape... Just drag reduction above hull speed.
     
  8. gonzo
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    gonzo Senior Member

    Dories and other double ended flat bottom boats plane easily.
     
  9. eric le marin
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    eric le marin naval architect

    Once again, planning is not the "stairway to heaven"

    Just have a look to what is going on with the US Littoral Combat Ship : one semi-planning monohull against a slim stabilized monohull (read trimaran with small floats) Both are going 50 knots with the same power.
     
  10. hoytedow
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    hoytedow Wood Butcher

    I wasn't trying to be funny. Gudgeon in wikipedia was very clearly defined. It is the ring into which the pintle is dropped. If you move the rudder from one end to the other, the pintle will travel but you would need 2 sets of gudgeons.
     
  11. tom28571
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    tom28571 Senior Member

    The answer is that, yes a double ender can plan in either direction. Some conditions must be met though. Must be able to plane in the first place and must have a mid section shape capable of giving enough lift to support planing in either direction. Of course, the rig and foils must also be capable of controlling the boat in both directions. I have come very near to planing a Laser stern first but control of the rudder was very difficult. Weight was forward and transom was clear of the water and course was very near dead downwind.

    Not sure why a boat would be wanted that would do this though.
     
  12. Inquisitor
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    Inquisitor Senior Member

    Thanks all for helping out.

    Tom,

    I can just imagine that being a handful sailing Laser backwards! Are you familiar with HarryProa's? http://www.harryproa.com/ They go both ways and the rudders/rig/everything are made to work either way, so they have to be symmetric front to back. Take a look at my #3 post... I'm just thinking out loud with this thread that there might be some speed advantages in that range where winds are not sufficient to get the windward hull out of the water... assuming that is... if a planing hull has less drag than a displacement hull in that region.
     
  13. tom28571
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    tom28571 Senior Member

    I did not find a link to the proa you mention. Of course. hulls of very high L/B ratio act differently and planing is rarely possible with most multihulls. The old "hull speed" axiom is not even applicable to them so it pays to ignore it. Some high L/B hulls do sport flattened aft sections that do promote planing in some conditions. I don't know whether this makes for overall lower drag though and the main purpose may be to prevent stern squat.

    Is there enough water and wind on Lake Lanier for your experiments? Silly question really and I spent many fine days sailing there in the past.

    Some of us used to sail short fun races where we were not allowed to point the bow of a Laser downwind. It made for an interesting windward mark. The reverse angle of the rudder made backwards steering super critical and was accomplished with a line tied to the tiller and held under high tension. In another fun race, we were not allowed to sit down or let the boom pass over our body. Tacking or jibing while passing behind the boom was sometimes interesting, especially on a planing reach.

    Edited to add that I see the link now. Also Chris Ostlind knows far more about multihulls than me and may drop in here.
     
  14. Inquisitor
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    Inquisitor Senior Member

    Its a breath of fresh air when constructive criticism is offered around here and someone doesn't assume a ***** is asking a question. Thank you Tom.

    Lake Lanier - Well these days, it is full versus seeing the town that is at the bottom of the lake. Last year, I damaged my daggerboard on an un marked concrete pier... centered the sucker. Crunch! As far as wind... so you know about our world dominating wind. :rolleyes: Passing gas makes the boat go faster. But, if I had any real wind, I'd have to shunt this boat every two minutes or so.

    So the backward trick was actually something you were cultivating versus just goofing off???

    Proa - Well just for the current academic thoughts of this thread and the decoupled nature of a Proa makes it OK to have the two hulls of wildly different characteristics. The lee hull build for speed and the windward to carry cargo and act as the sole counter weight.

    So, yes the L/B ratio of the lee hull is approaching 20:1, the windward hull is near a mono hull number of 6:1. I was just assuming at 6:1 that the old 1.34*sqrt(L) number does "kind of" apply. And with my wonderful winds, I'll spend a lot of time never getting near flying that windward hull... but wondering if it got above its hull speed (~8 knots) and could be made to plane, its drag would reduce and thus accelerate faster and have a higher transonic (joke) speed.
     

  15. hoytedow
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    hoytedow Wood Butcher

    No offense intended. I started on the assumption you knew what a gudgeon was. And you knew it was a fish, so anyway, sorry if my own lack of eloquence chaffed you in any way. I never thought you were a *****.
     
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